It is well known in the connector art to provide keying systems for connector assemblies. Keying systems enable, for example, particular plugs to be keyed with a specific keying configuration so that they may only be connected to receptacles having a complementary keying configuration. This is done typically for the purpose of preventing connection of a plug to a receptacle which does not have a keying combination complementary to that of the plug. A wide variety of keying systems for this and similar purposes are known in the connector art.
There are, however, certain drawbacks typically associated with known connector keying systems. Many such systems require permanent and irreversible alteration, that one or more of the connectors to be keyed to each other be permanently altered in some fashion. For example, keying of the connectors disclosed in U.S. Pat. Nos. 4,448,467 and 4,449,767 requires that removable keying tabs be fractured from the plug type connector. Keying of the assembly disclosed in U.S. Pat. No. 4 376,565 requires that one or more slots be cut through the receptacle connector of the assembly. While U.S. Pat. No. 4,376,565 discloses that a slot could then be filled by an insert, the alterations to the respective connector assemblies are otherwise irreversible.
The keying system disclosed in U.S. Pat. No. 4,376,565, in requiring slots to be cut in the receptacle portion of the assembly, suffers from the additional disadvantage that the receptacle may be weakened by the slots. As a result, the fit between the plug and receptacle portions and the stability of the connection may suffer.
The keying systems of the aforesaid patents, like many other keying systems known in the art, require an error prone procedure to build the keying system on the connector and to assure that the configuration of several different keying locations on the plug portion be correlated correctly with a corresponding number of positions on the receptacle portion of the assembly. For example, in the assembly disclosed in U.S. Pat. No. 4,448,467, any of several keying tabs may be removed by fracturing from the plug portion and key plugs must be inserted in the corresponding positions on the receptacle portion. A similar operation is required with the system disclosed in U.S. Pat. No. 4,449,767. Likewise, in the keying system disclosed in U.S. Pat. No. 4,376,565, keys may be inserted in grooves on the surface of the plug at any of several positions and corresponding slots must be cut in the receptacle. These plural operations, with the attendant checking and cross-checking the multiple keying positions, make the keying procedure a time consuming task.
In each of the keying systems described above, removable keying elements are assembled into either the plug or the receptacle in a direction corresponding to the direction in which the plug and receptacle are moved relative to each other during connection. The keying elements are removed by movement in the direction in which the plug and receptacle are moved during disconnection. This is typical of many keying systems known in the art and presents at least some danger that the inserted keying element(s) may be dislodged or removed as a result of being pushed or pulled upon during connection and/or disconnection of the plug and receptacle. Should this occur, the keying configuration of the assembly will be undesirably altered. The keying elements may not be fully visible to the user, such as in the system disclosed in U.S. Pat. No. 4,449,767, this presents a danger that the altered state of the keying configuration may go undetected. The fact that keying elements may be wholly or partially obscured from view presents an additional problem in that an operator may have difficulty discerning the particular keying configuration or keying combination of a plug and/or receptacle.
Thus, as noted above with reference to the aforesaid exemplary keying systems, there are various drawbacks typically associated with keying systems or connectors known in the art.
The above discussion makes reference to connectors which are specifically adapted for electrical conductors. Recent years have seen the increasing use of optic fibers for conducting signals in communications systems, computer systems, etc. Optic fibers are by no means identical to electrical conductors, and connections of optic fibers involve considerations not present in connection of electrical conductors.
Some systems employing optical fibers to conduct signals impose additional requirements upon the connections for the fibers beyond simple matching of the correct plug to the correct receptacle. One such requirement is correct polarization of the connected fibers when two or more optical fibers are used in signal-conducting cables. Keying is required in computer mainframes and other peripheral equipment in local area networks (LAN) that are envisioned from the start to be implemented exclusively with fiber optics. That is, the components or stations in each LAN are to be connected with one another exclusively by optic fiber cables.
Connection of the stations in such a manner requires that each station comprises one or more physical connections, each connection including an input path and an output path, to and from the station. Because the output of one station must be correctly connected to the inputs of the other stations, it is absolutely necessary that correct polarization of all physical connections be maintained at all times.
Additionally, in any particular LAN, it is necessary that stations be connected in proper sequence and/or proper arrangement. In order to avoid errors in sequence or arrangement, and to avoid improper connections between respective stations, connectors employed in the system must also include a keying system.
A keying system may require four or more keying combinations. Four of these are designated as configurations A, B, Master (M) and Slave (S). A requirement would be that a plug having the Slave keying configuration must mate to a socket or receptacle having any of the various keying configurations. The A, B and Master configurations in the plug must mate only to the corresponding configuration in the receptacle. This must all be accomplished with a connector assembly which properly aligns respective optical elements and/or optical fiber pairs.
U.K. Patent Application GB 2,069,175 discloses a connector assembly suitable for connecting duplex optic fiber cables to each other. The assembly includes a receptacle sleeve adapted to receive a plug in either end thereof. Each end of the sleeve includes a recess, and each plug includes a protrusion which fits into the recess. The respective plugs cannot be fully inserted into the sleeve unless the protrusion associated with each plug is properly aligned with the recess in the sleeve. Consequently, proper polarization of the connected cables is obtained.
However, the connector assembly disclosed in the aforesaid U.S. patent application comprises no means whatsoever for altering the keying configuration of the plug and/or sleeve.